An evaluation of WIPP structural modeling capabilities based on comparisons with South Drift data

The creep response of rock salt around a long uniform excavation of rectangular cross-section has been computed with the structural finite element code SANCHO, and the results are compared with field data. The excavation, known as the South Drift, is part of the Waste Isolation Pilot Plant (WIPP) facility. The geomechanical model used in the calculations is quite complex and includes constitutive models based on standard laboratory creep tests. Because closure and closure rate measurements are at least three times larger than computed values, a thorough investigation of the many parameters in the geomechanical model is presented. This investigation indicates that variations to parameters not related to the constitutive model for halite cannot produce the type of changes in the closure histories needed to produce good agreement with data. Thus, the reason for the discrepancy is attributed to the parameters in the constitutive model for halite. However, none of the halite parameters investigated could produce the measured behavior. Several areas for future study have been identified.